"It's a certified helmet. He's all-in and ready to go," Gruden told reporters. "That's my understanding. Really happy to have him out here. He's a great player."

League sources told NFL Media that Brown wore a Schutt Vengeance Z10 LTD helmet during practice. It is among the 34 helmets approved for use following laboratory tests conducted earlier in the year by the NFL and NFLPA.

Brown didn't have a helmet during the first portion of practice, according to NFL Media. He later took part in drills with the offense while wearing the approved helmet.

The star wideout filed a second grievance over his ongoing helmet issue. According to NFL Media, the same independent arbitrator from his first hearing will oversee the second. The grievance is scheduled for Friday morning.

"This grievance is no laughing matter," Gruden said. "It's important to him."

Brown left the team twice during the Raiders' training camp in Napa, Calif., due to issues with the usage of his old helmet and an accident in a cryogenic therapy chamber. He suffered frostbitten feet after failing to wear proper footwear while using the machine.

"He's really good," Gruden said. "He's shown great retention at what we're doing. He didn't miss the off-season program. He's been here and out of here in meetings. It's just good to have him back. He's in great shape. He's running hard and running good routes."